矩形通道干涸后膜态沸腾传热试验研究

在流动传热基础试验平台上进行了矩形通道干涸后膜态沸腾的传热试验,研究了各种热工水力参数对膜态沸腾传热的影响特性.结果表明:干涸后膜态沸腾是一个相对稳定的传热过程,其壁面温度不会出现明显的脉动;随着进口含汽率的增加,膜态沸腾热流密度减小,壁面温度升高,传热系数减小;随着质量流速的增大或系统压力的升高,膜态沸腾热流密度增大,壁面温度降低,传热系数增大.     

300MW循环流化床锅炉稀相区的传热研究

本文针对燃烧煤矸石的循环流化床锅炉的传热情况展开研究,以山西平朔电厂1台300 MW的循环流化床锅炉为实例,采用环核模型和颗粒团更新模型,对稀相区的传热系数分布进行建模计算,本文所建模型考虑炉内床温实际分布特征,根据现场温度实测数据对模型进行修正,研究了对流和辐射换热系数在不同负荷下沿炉膛高度的变化情况。锅炉在较高负荷下运行时,负荷的波动对颗粒团壁面覆盖时均份额影响较小,继而对炉内对流换热影响较小。炉内环形区温度沿床高的偏差随负荷升高略有减小,且对辐射换热影响比对流换热大。随着负荷升高,对流换热系数沿炉高下降增大,而辐射换热系数沿炉高下降减小,高负荷时炉内总换热系数沿炉高下降25%左右,低负荷时沿炉高下降28%左右,高负荷下炉内沿高度温差更小,传热更稳定。     

高温鼓泡流化床的流化行为

床层温度在20－1000℃范围内,以4种粒径的煤灰为实验物料,研究了不同表观气速下最小流化速度,床层平均空隙率,压力波动标准偏差和主频的变化规律,最小流化速度随床层温度升高而减小;相同床温下,平均空隙率随表观气速升高而增大,不同床温下,压力波动偏差随流化数增加而增大。相同流化数时,B类颗粒的压力波动标准偏差受床层温度变化影响较小,而D类粒子随床层温度升高压力波动标准偏差减小,胡着流化数增加,压力波动主频减小。     

颗粒帘换热器中颗粒空隙率的计算方法与实验研究

运用流动过程能量守恒原理与Ergun公式,推导出基于颗粒帘工况条件与运行参数的颗粒空隙率计算公式,并根据实验测试结果计算得到各工况条件对颗粒空隙率的影响规律.结果表明:颗粒空隙率沿下落行程呈现先减小后增大的规律;颗粒空隙率随进气速度及颗粒帘初始厚度的增大而增大,随颗粒粒径及颗粒质量流量的增大而减小;进气速度、颗粒帘初始厚度对颗粒空隙率的影响大于颗粒粒径、颗粒质量流量对颗粒空隙率的影响.     

微型燃气轮机CW原表面回热器芯体内传热及阻力特性分析

建立微型燃气轮机CW(交叉波浪型,Cross Wavy)原表面回热器三维周期性充分发展数值计算模型,对芯体内传热和阻力特性进行了分析,确定了质量流量和温度水平对换热量及压降的影响,给出了CW原表面芯体板内阻力、传热因子以及努塞尔数与雷诺数之间的经验关联式。传热及阻力性能分析结果表明:随着雷诺数的增大,回热器芯体单元传热系数增大,传热量逐渐增加,并且随着低压高温烟气侧的进口温度升高,传热量增加幅度增大;回热器芯体单元回热度随雷诺数的增大而减小,随燃气进口温度升高而减小。     

熔盐与过冷沸腾水传热特性实验研究

为研究熔盐蒸汽发生器的传热特性,以Solar Salt二元硝酸盐为工质,对熔盐与过冷沸腾水在蒸汽发生器中的传热规律进行实验研究.实验结果表明:熔盐传热系数随着水侧与熔盐的质量流速的增大而增大,随着水侧压力的升高而减小;当水侧在过冷水状态时,熔盐传热系数随着熔盐入口温度的升高而增大;当水侧在过冷沸腾状态时,熔盐传热系数随...     

高温型循环流化床锅炉炉膛传热系数的试验研究

为了测定高温型循环流化床(CFB)锅炉炉膛的传热系数,在热功率1MW的CFB锅炉试验台上对试验受热面的传热系数进行了试验和测定,研究了床温和颗粒悬浮密度对传热特性的影响.通过对试验数据进行回归分析得到了炉膛传热系数与床温和颗粒悬浮密度的关联模型.结果表明:随着床温的升高及颗粒悬浮密度的增大,炉膛传热系数相应增大;该关联模型得到的炉膛传热系数计算值与试验值的误差小于7%,该关联模型可用于高温型CFB锅炉的设计计算.     

钠冷堆非能动余热排出系统建模研究

非能动余热排出系统是核电站堆芯安全性的重要保障,为优化钠冷堆余热排出系统的热工设计方法,明确环境温度及空气冷却器结构变化对余热排出系统的影响。在考虑拔风烟囱自然循环影响的情况下建立完整的钠冷堆非能动传热模型,得到通用的余热排出系统通风量方程,并基于流动平衡和能量平衡对一定设计传热量的余热排出系统进行流程优化并分析环境温度、烟囱高度及翅高变化对系统热力参数的影响规律。结果显示,系统的总驱动压和总传热系数随着环境温度升高逐渐减小,且环境温度对驱动压力的影响更为明显;拔风烟囱高度增加,系统总驱动压和总传热系数均增大,且增大趋势不断变缓,存在设计最优值;翅片管翅片高度减小,系统总传热系数及单位压降传热系数大幅增加,对系统的传热性能影响明显。     

不同煤种燃烧过程中PM10排放特性的研究

在滴管炉(DTF)上对4种典型煤种进行了燃烧试验,研究了煤种、粒径、温度和停留时间对燃煤PM10排放量的影响.结果表明:无烟煤PM10排放量整体较小,烟煤PM1+排放量大,2种褐煤PM1-排放量较大,但PM1+排放量趋势不一致;粒径的影响因煤阶不同而差别较大,随粒径增大,烟煤的PM10排放量增大,而高阶褐煤的PM10排放量先增大后减小,低阶褐煤的PM10排放量变化不大;当最高燃烧温度高于灰熔融温度时,PM10排放量随温度升高先增大后减小;随着在高温区停留时间的延长,PM10颗粒物有小颗粒向大颗粒转化的趋势.     

不同煤种燃烧过程中PM_(10)排放特性的研究

在滴管炉(DTF)上对4种典型煤种进行了燃烧试验,研究了煤种、粒径、温度和停留时间对燃煤PM10排放量的影响.结果表明:无烟煤PM10排放量整体较小,烟煤PM1+排放量大,2种褐煤PM1-排放量较大,但PM1+排放量趋势不一致;粒径的影响因煤阶不同而差别较大,随粒径增大,烟煤的PM10排放量增大,而高阶褐煤的PM10排放量先增大后减小,低阶褐煤的PM10排放量变化不大;当最高燃烧温度高于灰熔融温度时,PM10排放量随温度升高先增大后减小;随着在高温区停留时间的延长,PM10颗粒物有小颗粒向大颗粒转化的趋势.     

Effect of pressure and temperature on cluster and particle heat transfer in a pressurized circulating fluidized bed

The present work reports the influence of pressure and bed temperature on particle‐to‐wall heat transfer in a pressurized circulating fluidized bed (PCFB). The particle convection heat transfer plays a dominant role in determining the bed‐to‐wall heat transfer coefficient. So far, no information is reported on the effect of pressure and bed temperature on particle‐to‐wall heat transfer in a PCFB in the published literature. The present investigation reports some information in this direction. The effect of system pressure and bed temperature are investigated to study their influence on cluster and particle heat transfer. The particle convection heat transfer coefficient increases with system pressure and bed temperature due to higher cluster thermal conductivity. The increase in particle concentration (suspension density) results in greater cluster solid fraction and also the particle concentration near the wall is enhanced. This results in higher cluster and particle convection heat transfer between the bed and the wall. Higher particle convection heat transfer coefficient results in enhanced heat transfer between the bed and the wall. The results will also help to understand the bed‐to‐wall heat transfer mechanism in a better way in a PCFB. Copyright © 2001 John Wiley & Sons, Ltd.     

Hydrodynamic and heat-transfer studies in fine particle gas-fluidized beds

A 0.152 m internal diameter fluidized-bed pilot-plant facility designed to operate up to a maximum temperature of 1500 K at ambient pressures has been fabricated, installed and tested. High temperatures are obtained by the combustion of propane-air mixtures in the bed. A specially designed bubble cap distributor plate ensures good gas dispersion and solids mixing in the bed.Preliminary measurements dealing with hydrodynamic and heat-transfer characteristics in the moderate temperature range 330–500 K at ambient pressures in beds of fine powders of sand, glass beads and alumina particles are reported here. These include the bed pressure drop and bed expansion as a function of fluidizing velocity and bed temperature. The characteristics of the bubble cap air distributor plate are also investigated in view of its role in controlling the quality of fluidization. The heat transfer between the bed and an immersed water-cooled vertical tube is analyzed to compute the heat-transfer coefficient and its dependence on the superficial air-fluidizing velocity and on bed temperature. These data are critically examined in the light of mechanistic processes taking place in the bed.     

Heat transfer between a fluidized bed and an immersed vertical U-tube

The design details of a 0.254 m stainless steel cylindrical fluidized bed pilot plant facility, whose fabrication, installation and testing have been recently completed, are described. It primarily consists of a fluidized-bed reactor, fluidizing air-supply system, solids feeder, off-gas cleaning and exhaust system, and cooling water-supply system for heat-transfer tubes provided in the bed and in the freeboard sections. The plant is operated at ambient pressure in the temperature range 300–600 K, both in the batch and continuous modes for solids feed. Bed-pressure drop measurements as a function of fluidizing velocity for two different bed heights reveal that the quality of fluidization is good. Similar experiments have been conducted with the continuous solids feed. The heat-transfer coefficient between the bed and an immersed stainless steel U-tube is measured as a function of fluidizing air velocity at five different temperatures. The effects on bed-to-tube heat-transfer rate of solids feed rate, bed height, air-flow rate, and bed temperature are examined. All of these observed variations are interpreted in terms of the solids mixing and bubble mechanics in the bed.     

Effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat

This paper reports the effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat. The unsteady model was set up, which has been applied to investigate the effects of particle sizes (1.77 mm–14.60 mm) on particle temperature, heat transfer quantity, overall coefficient of heat-transfer, etc. The heat transfer performance of waste heat recovery heat exchanger is improved when the particle size increases, which is conducive to increase hydrogen production. The particle temperature change rate, the specific enthalpy change rate, the moving velocity of the maximum heat release rate particle, the contribution rate of solid phases, the heat release rate and the overall coefficient of heat-transfer increase, but the effective time of heat transfer decreases. When the particle size increases from 1.77 mm to 14.60 mm, the solid phase average contribution rate increases from 89.43% to 94.03%, the overall coefficient of heat-transfer increases from 1.39 W m⁻² K⁻¹ to 13.41 W m⁻² K⁻¹, the heat release rate increases from 48.9% to 99.9% and the effective time of heat transfer reduces from 48 h to 6.7 h.     

CFD modeling of heat transfer of CO2 at supercritical pressures flowing vertically in porous tubes

Computational fluid dynamics (CFD) tool has been used for investigation of convective heat transfer of CO₂ in two porous tubes. Effects of some important parameters such as pressure, inlet temperature, mass flow rate, wall heat flux and porosity on temperature distribution and local heat transfer coefficients have been studied numerically. Near the supercritical conditions, these parameters are very effective on temperature gradient and local heat transfer coefficients. For example at p = 9.5 MPa, under the same conditions, the heat transfer coefficient in a tube with particle diameters of 0.1–0.12 mm is about 20–30% higher than when the particle diameter of 0.2–0.28 mm were used. The heat transfer coefficient increases with decreasing pressure and increasing mass flow rate. Also the porosity of the bed has the important role on the heat transfer. The CFD predictions have been compared to the experimental data and showed pretty good agreement.     

A combined GCMC and LBM simulation method for CH4 capture in Cu-BTC particle adsorption bed

Two-dimensional Lattice Boltzmann Method (LBM) combined with grand canonical Monte Carlo (GCMC) approach is proposed to investigate the heat and mass transfer of methane (CH₄) adsorption in Cu-BTC particle adsorption bed. In interfacial boundary, saturation adsorption capacities are obtained by GCMC method to replace empirical values. The diffusion and adsorption heat in particle interior are fully considered. Langmuir-Freundlich model and linear fitting formula are used to calculate the saturation adsorption capacities in Langmuir adsorption kinetics model and the adsorption heat in heat transfer in LBM model at mesoscopic level, respectively. At micro-scale level, GCMC method is used to obtain parameters of Langmuir-Freundlich and linear fitting formula. The effects of porosity and particle size on CH₄ adsorption are discussed. Results show that the time for the saturation adsorption decreases with an increase in porosity and increases with increased particle size. In fluid region and particle interior, temperature peak decreases with increasing porosity and particle size. Nonuniformity of temperature exists both in fluid region and solid particles. The adsorption properties in Cu-BTC adsorption bed, such as the relation between external and internal heat and mass transfer, is predicted intuitively by GCMC and LBM combined simulation method.     

Hydrodynamic and Heat Transfer Characteristics of Magnetofluidized Beds

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Simulation study of the effect of the restitution coefficient on interphase heat transfer processes and flow characteristics in a fluidized bed

This article discusses a simulation study performed to investigate the effect of particle collision on inter-particle and gas–solid heat transfer processes, and other related bed flow characteristics. The effect of particle elasticity is presented using different values of the particle–particle coefficient of restitution. The simulation study was carried out using a two-dimensional model of a fluidized bed reactor incorporated to ANSYS Fluent 16.2 software. Two different materials, steel beads and sand particles, were used as the bed material fluidized by air. The simulation results are compared to those from previous studies on fluidized bed reactors containing a single bed material. The coefficient of restitution affected the bed hydrodynamics. Specifically, an increasing coefficient of restitution resulted in an increasing bed pressure drop and decreasing void fraction, granular temperature, particle velocity, and collision frequency. Conversely, increasing the particle coefficient of restitution resulted in decreasing the particle–particle heat exchange coefficient and the gas–particle heat transfer coefficient. The gas–particle heat transfer coefficient for sand particles was higher than that for steel beads. The effect of the coefficient of restitution on the flow characteristics from a binary mixture bed was quite similar to those of single material beds found in previous studies. This study demonstrated that the restitution coefficient clearly affected both the particle–particle and gas–particle heat transfer processes.     

基于格子Boltzmann方法的饱和土壤渗流与传热数值模拟

本文利用随机多孔介质生成算法重构了与真实土壤外貌相近的多孔介质几何结构。通过引入不可压耦合双分布格子Boltzmann模型（lattice Boltzmann model ,LBM）对孔隙尺度下单相饱和土壤渗流和传热进行了模拟。着重讨论了不同渗流压差、孔隙率、土壤固体颗粒尺寸分布对流动与传热的影响。结果表明：土壤渗流速度与渗流压差呈线性单调递增关系,平均温度随渗流压差增加而增大,但温升速率逐渐减缓;当孔隙率增大时,渗流速度增加,且当孔隙率大于0.58时,对流换热作用迅速增强,土壤温升速率显著加快;对于相同孔隙率,当土壤固相颗粒尺寸较大时,流动出现典型优先流效应;随着土壤固相颗粒尺寸减小,土壤温度变化逐渐趋于平缓,平均温度降低。     

Profiles of hydrogen molar fraction and temperature in ZrV1.9Fe0.1 alloy bed for hydrogen absorption

Profiles of hydrogen molar fraction and temperature in a long ZrV_1.9Fe_0.1 alloy particle bed with a small diameter were determined experimentally and analytically as a basic study of chemical heat pumps operated at higher temperature. Since the alloy bed absorbed hydrogen even at $\text{873}\text{K}$ and generated heat, the alloy was considered a suitable material for heat pump or hydrogen storage at higher temperature. Experimental profiles of both hydrogen molar fraction at the bed outlet and temperature inside the bed agreed with analytical solutions to heat and mass transfer equations. The analytical solutions were obtained under the conditions where constant-pattern approximation could be applied to the temperature and concentration profiles propagating in a bed with the same velocity. Properties relating with heat transfer such as a heat capacity, enthalpy change of hydrogen absorption and a heat-transfer coefficient between a wall and particles were correlated to two dimensionless parameters, α and β.